This invention generally relates to liquid heating apparatus and, in a representatively illustrated embodiment thereof, more particularly relates to a specially designed heat pump water heater and associated control system.
In the past, various proposals have been made for operatively coupling a heat pump to an electric water heater to controllably add refrigerant heat to the water stored in the tank portion of the water heater during water heating demand cycles. Since the coefficient of performance of a heat pump is considerably better than the coefficient of performance of the electric resistance type heating structure of an electric water heater, this use of a heat pump provides an opportunity to substantially reduce the operating cost of an electric water heater to which it is operatively coupled, with the electric heating structure being available as a supplemental water heating mechanism should the heat pump fail or need heating supplementation.
As is well known in the water heater art, there is a tradeoff between the heating cost effectiveness of a heat pump and the more rapid water heating capability of an electric heating element. In conventionally constructed heat pump water heaters the user typically has little if any ability to selectively adjust the relationship between water heating cost effectiveness and water heating rapidity in the water heater to suit varying operating environments and hot water demand situations. An additional need that exists in the heat pump water heater area is the need for improvements in the placement and component arrangement of the heat pump portion of the water heater. It is to these needs that the present invention is primarily directed.